class SingleDog{
      show(){
        console.log('我是一个单身狗')
      }
      static getInstance() {
         if(!SingleDog.instance)
         {
             SingleDog.instance=new SingleDog()
         }
        1
         return SingleDog.instance
         
      }

}
const s1=SingleDog.getInstance()
const s2=SingleDog.getInstance()
console.log(s1)
console.log(s2)
console.log(s1===s2)